The ionosphere is a region of the earth's atmosphere beginning at about thirty miles above the earth's surface and extending up to about two hundred sixty miles. The ionosphere includes bands of free ions and electrons existing in sufficient quantities to effect the direction of electromagnetic wave travel. This characteristic of the ionosphere is utilized to propagate certain frequencies of radio waves for long distance radio communication.
It is known that the ionosphere can be modified in certain respects by heating it with powerful radio waves beamed up from the ground. Ionospheric heating provides a useful tool for aeronomy (the study of the upper atomsphere and especially of the ionized gas regions) and for the study of communications pathways. See, for example, G. Meltz and F.W. Perkins, "Ionospheric Modification Theory: Past, Present, and Future", Radio Science, Nov. 1974, pp. 885-888, and G. Meltz, L. H. Holway, Jr., and N. M. Tomljanovich, "Ionospheric Heating By Powerful Radio Waves", Radio Science, Nov. 1974, pp. 1049-1063.
In heating the ionosphere, enormously large amounts of continuous rf energy are required. The rf energy need only be at one frequency and no modulation is necessary. Due to the large amounts of rf energy that are required, a single transmitter is not feasible; instead distributed transmitter sources, having large numbers of transmitter units, are utilized. In designing the basic transmitter unit, the large number of transmitter units causes the cost per watt to become a dominant design factor. The number and type of active devices used in the transmitter unit have a significant impact on the cost per watt. Thus, there is a need for a transmitter unit that minimizes the number of active devices so that large numbers of the units can be inexpensively built.
The object of the present invention is to provide an inexpensive method and apparatus for generating and radiating electromagnetic energy for use in modifying the electrical characteristics of portions of the atmosphere.